There are two prior patent applications of mention above which discuss video fingerprint methods for video signals. The ""864 application by G. C. Copeland discloses a video fingerprint method that inserts a low frequency low level signal within the video signal, such that is not observable to the viewer, but is readily detectable by a special detection circuit. This low level signal operates over many fields in a manner that makes it possible to detect and identify the source of the signal. The disadvantage of ""864 prior art is that the fingerprint method may not be compatible with certain video compression systems. The ""613 application by J. O. Ryan and G. C. Copeland uses the concepts of the ""260 patent application for a scrambling system for various recording media.
EPO Application 0 690 595 describes a method and apparatus that encodes identification information into a stream of digital data representing an object. The digital data representing an object is modified to add embedded identification information into the data. This modification is done such that the resultant changes to the object are not objectionable to the user. By comparing the original data to the modified data, the possessor of the original data can recover the embedded identification information. However the identification information is effectively unavailable to anyone not possessing the original data.
There is a need for a secure video fingerprint method having the property that the fingerprinted video be compatible with the various video compression systems currently in use. In particular, it should be compatible with compression systems based on for example the Discrete Cosine Transform (DCT), which may employ inter-field redundance coding. Motion picture experts group (MPEG-1 and MPEG-2) are examples of such compression systems. In anticipated applications, the video signal generally is subjected to the processes of fingerprinting, compression, decompression and fingerprint detectionxe2x80x94in that order. The fingerprinted video therefore will be subjected to the processes of compression and decompression prior to fingerprint detection.
The fingerprint systems of previous mention may tend to disturb the inter-field redundancy in a television signal that the compression systems of previous mention depend upon for proper operation. When the inter-field redundancy is disturbed, the bit rate requirements for the compression system rise, possibly to an unacceptable level, for the transmission path of the compressed video signal. Therefore there is need for a fingerprint system that does not degrade the inter-field redundancy to a level that requires excessive bit rates to provide a given picture quality.
The present invention provides a fingerprint method and apparatus which overcomes the compression system incompatibility of the prior art fingerprint systems of previous mention, while further meeting other various desirable requirements such as not being observable to a viewer while conveying information in the active video signal.
In addition, the present invention meets requirements such as the following:
Video Standards
The fingerprint method and apparatus of the invention is applicable to either analog (NTSC, PAL, SECAM) or digital (CCIR-601) video signals.
Security
The present fingerprint method and apparatus intrinsically provides a high level of resistance to hacking. In other words, it is very difficult to remove the fingerprint from the video.
Invisibility
The present fingerprint method and apparatus primarily is intended to convey information in entertainment applications such as video movies, television (TV) shows, and the like. It is essential that the fingerprint method not affect the entertainment value of the video image while being securely concealed within the image, but must be readily detectable by, for example, a detection circuit in a disk or tape recorder or other signal processing apparatus.
General Video System Compatibility
In addition to the foregoing requirements and attendant advantages, for maximum operational flexibility, the invention ensures that the fingerprinted video signal appears as a normal video signal to most if not all video processing methods and devices designed to operate with unfingerprinted video signals, and the like.
In particular, the video signal""s fingerprinted in accordance with the invention is compatible with all video recording, transmitting and processing devices likely to exist in a production or editing environment. Passage of the fingerprinted video through these devices does not cause the fingerprint to be removed or be made more difficult to detect.
Further, the present fingerprint method and apparatus, or at least a particular embodiment thereof, is compatible with consumer video cassette recorders (VCRs). That is, the invention makes it possible to record the fingerprinted video signal on a consumer grade VCR, and replay it later for detection without any likelihood of it being removed during the record/replay process.
More particularly, the invention provides a library of warp patterns, each of which is capable of imparting a selected degree of local spatial distortion to a video image. In response to an operator""s selection, a pattern select code determines which stored warp pattern is supplied as a fingerprint signal to a warp engine. The warp engine in turn applies the selected warp pattern to the video image to correspondingly locally spatially distort the image. The slight distortion imparted by the selected warp pattern is not observable to a viewer, but is detectable by a circuit in a recording device to, for example, prevent the recording device from copying the video signal. Alternatively, the fingerprint also allows subsequently comparing the original unfingerprinted video signal and an unauthorized copy of the fingerprinted video signal, to determine the origin, date, etc., of the unauthorized copy. For example, in the event a fingerprinted video signal is illegally recorded onto a disk or tape, the spatial distortion imparted by the fingerprint technique remains with the recorded video image. Thus a subsequent comparison between the pixel positions of a fingerprinted signal (that is, an illegal copy) and the unfingerprinted original signal, can be used to identify the source of the illegal copy.